The Forming Mechanism and Mesoscale Analysis of Local Heavy Rainfall
By using regular meteorological observations data, regional automatic station observation data, Doppler radar data, 1°×1° NCEP 6 h interval reanalysis data and hourly FY2C satellite TBB data, the forming mechanism and mesoscale system activity feature of the heavy rainstorm seen in Shangqiu in 7-8 July 2012 are analyzed. The results show that the trough at 500 hPa and eastwest shear line in the low level are compatible with the lowlevel jet stream, forming the largescale circulation for the rainstorm. Mesoscale analysis shows that several convective cells develop into four rainfall centers, and the convective cells accompany the MαCS, which is merged and strengthened by some MγCS and MβCS. The MγCS and MβCS are triggered, generated and developed by the ground mesoscale convergent systems or convergence center. The movement and development of heavy precipitation echoes correspond better with ground moderate convergence systems. The rainstorm occurs after the formation of ground convergence system within 1-2 hours. The warming in some local areas caused by warm advection is the main cause for the formation of surface mesoscale convergence system. Rainfall intensity is proportional to the TBB gradient. When TBB/0.5°E≥34℃, and TBB≤-63℃, severe rainfall of 30 mm·h-1 would occur. When MCS (mesoscale convective system) gets matured, heavy precipitation occurs near the low TBB center of the mesoscale convective clouds and when TBB is lower than 31℃ in one hour, shorttime severe rainstorm of 50 mm intensity would appear in 1-2 hours. Therefore, the uneven local ground heat warming is the main cause of this moderate convergence system. Moreover, the development of ground moderate convergence systems trigger the evolution of mesoscale convective systems, leading to the generation of local heavy rainstorm. So according to the TBB intensity and the variation of mesoscale convective clouds, forecast of shorttime heavy rainfall can be made in advance of 1-2 hours.